Automatic cathode voltage adjusting device



March 25,1941. l.. J. McKEssoN AUTOMATIC CATHODE VOLTAGE ADJUSTING DEVICE Filed Deo. 15, 1938 2 Sheets-Sheet 1 .4.6. F/LAMEN T D. C. PLATE SUPPL Y SUPPLY INVEN TOR. ./.EW/.S'JVc/{ESSON A TTORN EY.

March 25, 1941. L. J. MoKEssoN AUTOMATIC CATHODE VOLTAGE ADJUSTING DEVICE Filed Dec. l5, 1938 2 Sheets-Sheet 2 D.C. PLATE 5UPPLY+ w 3 7 /Z/T /sg kSbNSv MRS:

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ATTORNEY.

Patented Mar. 25, 1941 AU'roMA'rrc os'rnona VOLTAGE AnJUsTrNG DEVICE Lewis J. McKesson, Port Jefferson, N. Y., assignor to Radio Corporation of Delaware of America, a corporation Application December 15, 1938, Serial No. 245,838

3 Claims.

This invention relates to a power supply for a thermionic discharge tube and, more particularly,to a means for automatically adjusting the voltage applied to the thermionic cathode in ac- 5 cordance with the space discharge current through the tube.

In present radio transmitters and in other circuits using thermionic discharge tubes .the lament voltage of the thermionic discharge tube is adjusted to a fixed value depending upon the maximum emission desired from the cathode. Under such conditions the filament voltage is established at the value corresponding to maximum emission and this voltage remains constant even though the emission is reduced or made zero by cutting oil' plate current. In actual practice this condition may-be especially bad due tol poor power supply regulation. Under such conditions the filament voltage will actually decrease with an increase in plate current.

An object of my invention is to overcome the heretofore mentioned difliculties.

Another object of my invention is to providel a means for automatically adjusting the filament voltage of a thermionic discharge tube in accordance with the space discharge current through the tube.

Still another object of my invention is to increase the useful life of vacuum tubes in radio transmitters and other services by automatically adjusting the emission capability of the cathode in accordance with the space current through the tube.

Briey, my device consists of a means for varying the voltage supply to the filament of a thermionic discharge tube in accordance with the plate current of the tube. 'I'iiis may be done either by means of a variable impedance which is automatically varied in accordance with the plate current, or it may include a number of xed impedances of different values which may be selectively switched into the lament circuit in accordance with the platecurrent of the tube.

A more complete understanding of my invention will be had by reference to the following detailed description which is accompanied by drawings in which Figure 1 illustrates an embodiment of my invention, while Fibure 2 illustrates a modification of the form of my invention shown in Figure 1, while Figures 3 and 4 show further modifications of my invention.

Referring, now, to Figure 1, reference numeral I represents a thermionicodischarge tube having a. plate 2, a grid 3 and a iilament 4. Obviously, the filament 4 may be replaced by an indirectly (Cl. Z50-27) heated cathode having a heating lament. if desired. The lament 4 is energized through a filament transformer 5 which is connected to the A. C. filament supply line l, I through a variable resistance 6. The variable resistance is used to flx the maximum operating value of the voltage supply to the filament 4. Also, in series with the filament transformer and the filament supply In a saturation choke coil 8; This choke coil comprises an iron core having wound thereon windings 8 and I0. These windings are on the outer legs of the coil and arranged in opposing relationship. On the center leg of the iron core is wound a direct current Winding Il. The relationship of thewlndings 9, I0 and Il is such that zero voltage is induced in the center coil which is designed to carry the direct current. The coil Il is connected between the center tap oftransformer 5 and the' negative side of the direct current plate supply I2. The positive side of the plate supply is connected through choke I3 to plate 2. Variations in the plate current to the vacuum tube I will induceequal and op-` posite voltages in the outside coils 9 and I0 of the saturation choke coil 8. The direct current in the center coil Il varies the magnetic flux through the closed magnetic circuit which, due to the variation in the slope of the saturation curve of the iron core will in turn vary the inductance of the alternating current coils 9 and Ill and thereby vary the effective impedance and the current flowing therethrough. This action is such that an increase in the plate current to the vacuum tube reduces the impedance of the unit and produces a higher filament voltage across the terminals of filament 4.

'By means of a variation in the dimensions of the saturation choke coil, the variation in voltage may be adjusted to follow any predetermined' law. Also, by insertion of variable resistors. air gaps or magnetic shunts, lthe designs may be adjusted to give various degrees of controlling action. i

Figure 2 shows a modification of the embodiment shown in Figure 1 which is particularly adaptable for use in cases where the anode current of the vacuum tube is of itself insuilicient to be used indirectly as a controlling force. An example of a -tube of this type is an X-ray tube. In this modification a fixed resistor I4 is placed in series with the direct current plate supply. The voltage drop through this resistor I4 is then applied to a direct current amplifier I5 and the resultant amplied direct current is then applied across coil Il. Except for this variation, the

modification shown in Figure Figure 1.

In certain cases in order to save space and re- 2 is the same as in duce losses it may be desirable to combine the secondary l5. On the same core with these two windings are two additional windings Il and ll Winding Il is connected through a resistance 3l.

to an auxiliary D. C. supply 32. 'I'he variable resistance I6 is suitably adjusted so that the core of transformer 3l is saturated to the proper extent to reduce the filament voltage to the re'- quired no load condition. Winding 3l is connected in series4 with the direct current plate supply to the thermionic discharge tube l and serves a similar purpose to that served by coil Ii in Figure 1. Coil 3l is so polarized as to buck the winding 3l'. rent through coil 3| effectively decreases the saturation of the core of the transformer 34 and thereby causes an increase in the current applied to filament 4. If desired, a condenser C may be placed across coil 3i or a lter interposed in this circuit in order to prevent any possibility of hum modulation of the plate supply by alternating currents induced in coil 3 I.

Another embodiment of my invention, which does not involve, the use of any direct current saturating coils, is illustrated in Figure 4. .In this modification a transformer 40 has one winding 40 connected in series between the filament transformer 5 and the alternating current filament supply 1, 1. The other winding 4l of transformer 40 is connected in series between the plate transformer 43 and the alternating current supply 42 of the plate. 'The secondary of plate transformer 43 is connected to rectifier 44 and the output of rectifier 44 is applied to the plate circuit of thermionic discharge tube I Ain the conventional manner. Across winding 4| of transformer 40 is connected a variable resistance 46. The two windings of transformer 4l are so poled that as the'current drawn from lthe alternating current plate supply 42 is increased an additional voltage is applied in series with the filament supply 1, 1 by means of the winding 40', thus adjusting the filament voltage to the needs of the tube under the increased load. By means of variable resistance 44 connected across the winding 4I it is possible to adjust the compensation to the required amount. v

As a further modification within the scope of my invention, saturation chokecoil I may be replaced by a relay so connected that a series lresistance in thefl1ament supply circuit is short circuited or the ratio of an auto transformer in the filament supply circuit adjusted by an increase of plate current. If desired, where polyphase filament supply is used the saturation reactor for each leg of the filament supply may be combined into a single structure using only a single direct current magnetizing coil.

Therefore, an increase of cur- While I have particularly described my invention with respect to vacuum tube devices such as used in a radio transmitter, it is obvious that my device may be applied to various other types of vacuum tube devices such as rectifier tubes of either the vacuum or gaseous types, cathode ray tubes, X-ray tubes, bombardment tubes, or any other such device in which space current is drawn intermittently and in which it is desired to increase the life of the cathode or filament.

While I have described and shown several modincations of my invention. it should be clearly understood that other modifications within the scope of my invention may be made.

I claim: 1. In combination, a thermionic discharge tube .having at least an anode and a cathode, a source of alternating current for energizing said cathode, a rst source of direct current for said anode, a transformer interposed between said source of alternating current and said cathode, said transformer having a pair of auxiliary windings, a second source of direct current for energizing oneofsaid windings, the other of said .windings being connected between said first source of direct current and said cathode, said auxiliary windings being arranged in bucking relationship whereby an increase in the anode current of said tube causes an increase in the voltage applied to said cathode.

2. In combination, a thermionic discharge tube having at least an anode and a cathode, a source of alternating current for energizing said cathode. a first vuource of direct current for said anode, a transformer interposed between said source of alternating current and said cathode, said transformer having a pair of auxiliary windings, a second source of direct current, means for energizingl one of said windings from said second source of direct current, the other of said auxiliary windings being connected'between said first source of direct current and said cathode, said auxiliary windings being arranged in a bucking relationship whereby an increase in the anode current of fsaid--tube causes an increase in the voltage applied to saidY cathode.

3. In combination, a thermionic discharge tube having -at least an anode and a cathode, a source of alternating current for energizing said cathode. a vfirst source of direct current for said anode, a tramformer interposed between said source of alternating current and said cathode, said transformer having a pair of auxiliary windings, a second source of direct current, means for energizing one of said windings with direct current `from said second source, the other of said auxiliarywindings being connected between said first source of direct current and said cathode, said auxiliary windings being arranged in a bucking relationship whereby an increase in the anode current of said tube lcauses an increase in the voltage applied to said cathode and means connected to said other auxiliary winding for preventing alternating currents induced therein from modulating said anode current.

' LEWIS J..McKESSON. 

